This invention relates generally to diagnostic ultrasound medical imaging systems, and more particularly, to methods and apparatus for detecting nonlinear echoes from contrast agents.
Contrast agents (e.g. micro-bubbles) can be used in diagnostic medical imaging to aid in the detection/classification of diseased tissues. In some detection methods, the nonlinear response of the contrast agent relative to tissue is used to distinguish between ultrasound echoes resulting from the presence of contrast agent and echoes resulting from tissue. For example, contrast agents may be used to boost blood echo signals in blood vessels.
Pulse inversion harmonic contrast imaging is an ultrasound contrast imaging method where two pulses having the same amplitude and 180 degree phase shift are transmitted to the body. The signal is detected in the harmonic frequency, which is twice the transmit frequency. Another method is amplitude modulation contrast imaging where pulses with different amplitudes are transmitted to the body. The signal is detected in the fundamental frequency. Other methods of contrast imaging are desired to improve the image quality when using various contrast agents.